For registering limit levels a filling level and/or limit level measuring device with a flexible connecting piece is known, wherein a transmitting and/or receiving device is accommodated in a housing, there being an oscillating element attached to the transmitting and/or receiving device via a flexible connecting piece. The oscillating element together with the transmitting and/or receiving device forms an oscillator. The mechanical oscillations of the oscillating element are damped when bulk material is present. The oscillation damping therefore functions as an indicator of the presence of product at the measuring point, and is converted into a limit level reporting signal by means of a device connected down-line.
The flexible connecting piece is constructed in the nature of a cable made of a synthetic material. Up to now, however, such arrangements have had operating temperatures only up to a maximum of 160° C. The flexible connecting piece is usually connected to the transmitting and/or receiving device, an extension pipe or the oscillating element with a flange, a screw-in connector or other fitting as connecting device, with commercially available plastic hoses or special lines being used as the flexible connecting piece, which are for the most part provided with an internal supporting strand that is anchored below in the oscillating element and above in a fitting on the housing or extension pipe.
Such arrangements have a great many disadvantages. Some present cables with an internal wire rope are very stiff. Conductors or lines even for applications at high temperatures of 160° C. are generally positioned outside and are not protected further. The conductors of the flexible connecting piece lie or hang like a cable with the synthetic exterior jacket directly in the bulk material or medium of the container, and are subjected directly to abrasion or wear by the bulk material. In addition, sufficient conductivity of the outer jacket of the cable is not implementable or present with all synthetic materials. Such a cable made of PUR (polyurethane) is provided with a conductive outer jacket with a surface impedance of <109 ohms. A disadvantage is that it is not always possible to prevent kinking of a synthetic cable made in this way. A complex 100% conductive connection must be produced by means of a grounding wire with a fixed connection between the oscillating element and the attaching element by welding or screw connection. In addition, even then the lines are only of limited usability at higher temperatures, if they are moved when in the installed state and do not follow a fixed routing.